Conventional camera systems are known having a function of performing exposure control operation based upon exposure measurement results obtained from metering mode mainly at a centerweighted metering, an evaluative metering, a multi-segment metering, etc.
For example, a technique is described in Japanese Unexamined Patent Application Publication No. 2001-54014, which combines the multi-segment metering and the adjustment of the gradation conversion properties. Such an arrangement provides suitable exposure for the principal subject, and provides an image signal with a suitable gradation representation.
Also, a technique is known in which independent gradation conversion processing is performed in increment of divided regions, which is generally referred to as “space-variant gradation conversion processing”. Examples of such techniques include a technique disclosed in Japanese Patent Application No. 3465226. A technique is described in this Application publication, which divides a image signal into multiple regions based upon texture information, and a gradation conversion curve is obtained for each region based upon a histogram so as to perform gradation conversion processing. With such an arrangement, gradation conversion processing is performed such that the background region is displayed with suitable exposure as well as the principal subject, thereby providing a high-quality image signal.
Also, a technique is known, which acquires the subject information as it is in a wide dynamic range by performing shooting multiple times under different exposure conditions. As an example of such techniques, a technique is described in Japanese Unexamined Patent Application Publication No. 2002-223387, which controls shooting conditions of shooting performed multiple times under different exposure conditions based upon the information acquired from pre-shooting which is performed beforehand prior to the real shooting. Such an arrangement allows suitable exposure conditions to be set for the subjects having various kinds of dynamic ranges, thereby acquiring information with respect to the subjects without redundancy.
Also, a technique is described in Japanese Unexamined Patent Application Publication No. 2005-175718, which dynamically estimates the noise amount with respect to the luminance signal and the noise amount with respect to the color difference signal so as to perform high-quality noise reduction processing.
The aforementioned technique described in Japanese Unexamined Patent Application Publication No. 2001-54014 provides suitable exposure and suitable gradation representation with respect to the principal subject. However, with such a technique, the other region, i.e., the background region is displayed under an exposure condition according to the principal subject, leading to a problem in that such a technique does not ensure suitable exposure control operation for the background region.
Also, with the aforementioned technique described in Japanese Patent Application No. 3465226, gradation conversion processing is performed for the regions effectively acquired in the shooting, thereby providing high-quality image signals with respect to such regions. However, with such a technique, “whiteout” regions in bright regions and “blackout” regions in dark regions, where the data cannot be acquired in the shooting, cannot be corrected, which is a problem.
Also, with the aforementioned technique described in Japanese Unexamined Patent Application Publication No. 2002-223387, shooting is performed under an exposure condition suitable for the dynamic range of the subject. However, with such a technique, optimum exposure control operation is not performed giving consideration to the subsequent gradation conversion processing and the effect of the noise in a dark region.
Also, with the aforementioned technique described in Japanese Unexamined Patent Application Publication No. 2005-175718, the noise reduction processing, the gradation conversion processing, and the exposure control processing are performed independently, failing to perform optimal cooperation of such a processings.
The present invention has been made in view of the aforementioned situation. Accordingly, it is an object of the present invention to provide a camera system which acquire the overall dynamic range suitable for both the principal subject and the background region, thereby providing a high-quality image signal effectively using the dynamic range of a scene.
Furthermore, it is another object of the present invention to provide a camera system which provide a subjectively preferable image signal giving consideration to “whiteout” in a bright region and the effect of the noise in a dark region.